Reuters wrote:... Another person familiar with the engineering work said the box would be made of stainless steel nearly half an inch thick.

It would be capable of containing an explosion, and would have a tube to vent smoke and flame outside. However, the source said engineers have raised questions about the safety of venting flames outside the plane, especially if it is on the ground and being fueled. The effect could be something like a flamethrower, this person said.

Great. So we're going to have 787s lighting farts whenever the batteries fail!

Was a smart move for an Airbus - you can definitley save weight elsewhere while giving more time for battery manufacturers to resolve this issue or come up with different battery type, not as "fragile" and "violent" as current Li-Ions.

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JohnC wrote:Exploding cars?!!! Where? When? Electric cars usually have a proper cooling/heating system for these, it would be hard for teh batteries in them to overheat and explode during normal use...

IIRC there were a handful of fires involving Chevy Volt battery packs following various types of accident testing. The most notable one, which occurred after a car had been crash tested and then put into storage, apparently occurred as a result of leaking battery-system coolant causing corrosion and finally leaking into the battery system.

Lower energy density, and IIRC can't be charged/discharged as quickly. Still, that seems to be a worthwhile tradeoff on something that can cause serious problems for an aircraft in flight.

Mostly just an engineering problem though. As they get more experience, this sort of thing will be validated well.

I'd imagine when they first decided to put jet engines for passenger planes they were thinking too much power packed in with the danger of the turbines shattering and shredding everyone nearby for instance.

Lower energy density, and IIRC can't be charged/discharged as quickly. Still, that seems to be a worthwhile tradeoff on something that can cause serious problems for an aircraft in flight.

It's not a tradeoff if it stops the plane from functioning. Boeing went with an "all electric" design for the 787 - flight control and heating is electrically powered instead of traditional hydraulic/pneumatic systems. As a result, the electrical power draw of the 787 is 5x that of regular planes. Without the high energy density of Li-Ion batteries, the 787 will need to be essentially redesigned - new flight control, heating systems and substantially increased plumbing, all of which will need to be recertified, not to mention add a lot of weight to the airframe, which might also have to be redesigned to handle the greater loads.

You can argue about the wisdom of pushing forward with such a risky move (going all electric) in the development phase of the aircraft*, but for now, Boeing is stuck with the 787 in its current form, and for the sake of its existing customers who have planes on the ground, Boeing needs to get the plane back in the air. A longer term solution will hopefully be next, maybe changing battery chemistry to something like LiFePo instead of LiCo (which is less flammable but also has less energy density than LiCo), or reducing the available battery power on the aircraft, which might affect its ETOPS range certification and limit the routes it can fly (which won't make customers - the airlines - happy either). Even changing the battery chemistry or cell layout will probably lead to substantial rework for Boeing and the FAA, as the structure will have to be recertified to the increased weight of a battery change, and may need to be redesigned.

* Some say that this was the product of ex-VPE Alan Mullaly (now CEO of Ford) who pushed the all electric paradigm. As with any radical shifts, there were no doubt opposing groups internally who resisted this idea, and you can bet that there are a lot of "I told you so"s going around inside Boeing right now.

PS It's also worth mentioning that to move to a traditional bleed-air powered aircraft, the engines on the 787 would have to be redesigned with bleed air systems and hydraulic + pneumatic compressors and shafts, which would be a major undertaking for both boeing and the engine manufacturers (Rolls and GE). So it's definitely the least attractive option (economically, technically and time-wise) for Boeing.

ChronoReverse wrote:I'd imagine when they first decided to put jet engines for passenger planes they were thinking too much power packed in with the danger of the turbines shattering and shredding everyone nearby for instance.

The first passenger jet aircraft, the De Havilland Comet (DH-106), had four jet engines buried in the wing instead of in today's ubiquitous under-wing pods.

The plane is electric and powered by the generators on the engines rather than bleed air and hydraulic pumps on the engines. This is unrelated to the battery used to start the APU being a lithium ion one. They went for lithium ion because it is lighter and smaller for the same amount of power so they use less fuel lugging it around the skies over the life of the plane and can carry more useful stuff. During certification there was a problem with one of the power distribution panels - that might have been a reason to go less electric but the current issue is different.

As Ned points out, a lot of early planes had engines buried in the wing. This causes big problems with engine fires and failures affecting adjacent engines - as an example last year the Vulcan ingested a silica gel sac on one engine which damaged it. That engine promptly blew the compressor blades out the front where they were sucked in to the adjacent engine and damaged that one as well. One of the disadvantages of the underwing podded engines is the pitch power couple. In a twin engined plane you have 100% more power than needed, in a go-around if you go to full throttle too quickly you can end up pitching up too far and stalling.

notfred wrote:I think Voldenuit is throwing the baby out with the bath water.

How am I throwing the baby out with the bahwater?

I said specifically that the best course of action for Boeing and fir its customers is to get the plane back in the air, preferably with as few changes to the aircraft and battery as possible/necessary.

Once the plane is flying again, a longer term fix is desirable, and I outlined the difficulty in major changes in configuration to the aircraft and the undesirability of doing so.

The 787 was conceived as an 'all electric' plane and designed as such. The best fix would be to make it as safe as possible while keeping it in this vein.

notfred wrote:The plane is electric and powered by the generators on the engines rather than bleed air and hydraulic pumps on the engines. This is unrelated to the battery used to start the APU being a lithium ion one. They went for lithium ion because it is lighter and smaller for the same amount of power so they use less fuel lugging it around the skies over the life of the plane and can carry more useful stuff.

Actually it's still related. Because the plane is all electric, there still needs to be enough electric energy to power the flight control surfaces and/or deicing system in the event of an engine failure. The high energy requirements necessitated the use of a high energy battery system. While you are correct that the battery fires so far have been on the APU battery (which is mainly designed to be used while on the ground), the main aircraft battery uses the same chemistry as the APU battery (offhand, I don't know if it's the exact same battery configuration).

ADDENDUM: Airbus is able to go to a lower energy density Ni battery because the A350 does not have the power draw requirements of the 787 since it's still a traditional bleed air design. While going Ni instead of Li will still result in a weight and/or range penalty, it won't be as disastrous to the flight capabilities of the A350 as it would be to the 787 (not to mention the A350 is still in development and would be able to absorb/implement changes in configuration with less engineering and regulatory overhead than a plane that has already rolled out). Of course, since the real engineering details of both aircraft are proprietary, I haven't done the math on this and am only providing my conjecture and assessment as an aircraft engineer of 7 years' experience on both Airbus and Boeing airplanes. Also, I'm not an APU or battery specialist, so take what you will from my opinions.

If you're interested in further details on this topic, you should check out teh Wiki article, it has lots of relevant info with cited sources... Of course, if you have something else to add in - don't be afraid to do that there:http://en.wikipedia.org/wiki/Boeing_787 ... y_problems

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ChronoReverse wrote:I'd imagine when they first decided to put jet engines for passenger planes they were thinking too much power packed in with the danger of the turbines shattering and shredding everyone nearby for instance.

The first passenger jet aircraft, the De Havilland Comet (DH-106), had four jet engines buried in the wing instead of in today's ubiquitous under-wing pods.

Exactly and eventually they found out the disadvantages of that and now all the planes use the pod design. It's something they'll figure out eventually. Perhaps just having the metal tub around it is all that's needed.

ChronoReverse wrote:I'd imagine when they first decided to put jet engines for passenger planes they were thinking too much power packed in with the danger of the turbines shattering and shredding everyone nearby for instance.

The first passenger jet aircraft, the De Havilland Comet (DH-106), had four jet engines buried in the wing instead of in today's ubiquitous under-wing pods.

Exactly and eventually they found out the disadvantages of that and now all the planes use the pod design. It's something they'll figure out eventually. Perhaps just having the metal tub around it is all that's needed.

For safety, maybe, but for the systems that require the battery it doesn't help. An article did mention there's a deployable 'ramjet' style generator to provide power in flight least. Replacement with a less volatile battery type will be the best solution.

It's too bad such an issue came up, but good that it came up earlier rather than later. It's easy to rag on Boeing for choosing this battery type, maybe some day we'll find out the details of the internal decisions, but as advanced and groundbreaking as the 787 is in so many ways, if this is the worst teething problem I'd call the program a big success. Thankfully there were no disasters because of it though.

Sorry Voldenuit, misread your post as suggesting the fix for the APU battery issues was to go back to the traditional design.

I'm still not entirely sure that the main battery needs to be that much more powerful than on a traditional type. Do you have a reference for this? The following is my understanding, please correct me where necessary given your experience.

On a traditional type wing deice is bleed air and flight control actuators are hydraulic. If you loose the engines then you've lost bleed air, and once the airspeed drops below windmill speed then hydraulic and generator power as well. By this point you need the APU up and running already otherwise you are on to the ram air turbine. In a traditional type the RAT will provide both electric and hydraulic power. As far as I'm aware, the main battery is only to keep the avionics up and running for 30 minutes so that the crew has basic instruments and radios to get the plane down safely.

In the 787 in the same scenario I think the same thing is going to be true, it will be APU or RAT powering the flight controls rather than the main battery. It simplifies the design of the APU and RAT as these now are purely electrical generators rather than needing to provide hydraulic pressure as well. In the case of the APU on a traditional setup it needs to provide bleed air for cabin pressurisation and main engine start, these are now electric on the 787 so no need for those extra bits on the APU. The main battery would still be just the avionics in this scenario.

I do think the movement towards an electric plane is a good thing considering the fume incidents that have happened with bleed air pressurisation and it should simplify the systems design - you just need electricity rather than electricity, hydraulics and bleed air. However Boeing seem to be finding this transition hard.

JohnC wrote:Exploding cars?!!! Where? When? Electric cars usually have a proper cooling/heating system for these, it would be hard for teh batteries in them to overheat and explode during normal use...

IIRC there were a handful of fires involving Chevy Volt battery packs following various types of accident testing. The most notable one, which occurred after a car had been crash tested and then put into storage, apparently occurred as a result of leaking battery-system coolant causing corrosion and finally leaking into the battery system.

notfred wrote:Sorry Voldenuit, misread your post as suggesting the fix for the APU battery issues was to go back to the traditional design.

No probs, I was pretty wordy and perhaps not all that clear.

I'm still not entirely sure that the main battery needs to be that much more powerful than on a traditional type. Do you have a reference for this? The following is my understanding, please correct me where necessary given your experience.

On a traditional type wing device is bleed air and flight control actuators are hydraulic. If you loose the engines then you've lost bleed air, and once the airspeed drops below windmill speed then hydraulic and generator power as well. By this point you need the APU up and running already otherwise you are on to the ram air turbine. In a traditional type the RAT will provide both electric and hydraulic power. As far as I'm aware, the main battery is only to keep the avionics up and running for 30 minutes so that the crew has basic instruments and radios to get the plane down safely.

Actually, planes have been gradually going electric for some time. The Airbus A380 for instance uses electrically powered backup flight control systems. It's just that the 787 uses more electric controls than previous aircraft. It's also worth noting that while only 2 of the main controls of the 787 are purely electric - the spoilers and horizontal stabilizer, the hydraulic power to the rest of the controls is generated electrically (I believe) on the 787 instead of mechanically from bleed air, so the 787 still does rely on electrical power a lot more than normal.

In a hydraulic system, there are hydraulic accumulators that store pressure and can provide continued pressure (and thus power) to the flight control surfaces in the event of total engine failure. The batteries on an electric aircraft provide the same function, acting as capacitors, if you will, in the event of loss of electrical power. So they would be sized to the requirement to power the critical electronics and control surfaces for emergency landings without power.

The second pushing factor for the battery size would be Extended Operations (ETOPS) rating. The FAA certifies certain twin engine plane types to be able to fly certain routes (I'm being a bit imprecise here, but bear with me) based on how long the plane can be certified to fly with one malfunctioning engine.Typical ETOPS ratings for twin engine aircraft are 180 minutes. In other words, a plane with an ETOPS rating can fly routes that place them within 180 minutes of an airport (for emergency landing) at any time. The 787 was designed to achieve an ETOPS rating of 330 minutes (currently, only a select few 777 variants have this rating). This means that in the event of a single engine failure, the combined energy available for flight controls (from the remaining engine, Ram Air Turbine, APU and both the main and secondary battery) would have to supply at least enough power for 330 minutes. Moving to a smaller battery would reduce the total available energy, and reduce the ETOPS rating for the aircraft. This might lock some routes out that were previously available to the aircraft, which would hurt the customers (the airlines).

Efficient weight usage is paramount in modern aircraft design, and I would say that the 787 has been optimized with a battery that's pretty close to what it needs for normal and emergency operations. Moving to a different battery chemistry or radically redesigning the existing cells would reduce the operational capability of the aircraft, which might make it less desirable to some customers. Because the 787 is more reliant on electrical power than competing aircraft, any change to its batteries would have a larger affect on the capabilities of the aircraft than on other planes.

Again, take what I've said here with some grains of salt. I'm not an expert in the specific areas of this discussion (emergency flight controls, power distribution and storage systems) or with the specific systems of the 787 in question. But I think I'm not too far off the mark when answering the question of "why doesn't boeing just move to a smaller/safer battery?". Oh, and lastly, certifying a completely new battery would probably take months if not years with the FAA, so a stopgap solution (containment structure, perhaps tightening QC on the battery manufacturer, more electronic safeguards on charge/discharge cycles) is pretty much what is needed right now. It may not be ideal, but with ANA having to cancell 1,800 flights because of the 787 grounding, it's what's needed. And at the very least, it has to be shown to be safe (as considered by both the FAA and Boeing) before it will be let back into the air.

Wow, so the FAA has approved the certification plan for the battery fix. To be clear, this just means they're approving Boeing to move on the the next stage of testing on the redesigned battery containment and isolation system, not necessarily approving the fix itself. If and when it is proved safe, then the changes would be approved and the plane recertified to fly.

Although I went on record as saying that this fix would be the quickest and most expedient way for Boeing to get the planes back in the air, I must admit that I am a bit disappointed in the FAA here. I was honestly expecting them to kick the idea back to the curb. The problem is that I frankly think this is a stopgap solution (as I said earlier), but that the management at Boeing doesn't seem to realise this. Once this is approved, they are likely to stop working on a more permanent solution until the next disaster happens.

Voldenuit wrote:Although I went on record as saying that this fix would be the quickest and most expedient way for Boeing to get the planes back in the air, I must admit that I am a bit disappointed in the FAA here. I was honestly expecting them to kick the idea back to the curb. The problem is that I frankly think this is a stopgap solution (as I said earlier), but that the management at Boeing doesn't seem to realise this. Once this is approved, they are likely to stop working on a more permanent solution until the next disaster happens.

You seriously expected the FAA to ground all 787s, the newest plane from the sole airliner manufacturer in the US, for an indeterminate period in the face of competition from the A350? There are many things I could say about the FAA, but they're all R&P.

Maybe this needs to be split off into another thread, but what is the benefit of having electric power over hydraulic design for control surfaces? It seems that in the event of Things Going Horribly Wrong, you'd want the plane to rely on as little electronics as possible.

Ahh the comet was a beautiful plane. Too bad the original square windows allowed stress cracks along with catastrophic decompression bringing down at least 2 planes. It was fixed when they installed round windows. Also the in wing engine design looks fantastic, but reduces fuel load and increases the chances of crashing if a turbine blows apart.. like taking out the engine right next to it fuel tanks and hydralic lines etc.Engine pods are much safer and, make the engines easier to maintain or replace/repair.

But i still think the comet was one of the best looking passenger planes of all time.

I'm always amused when the topic of electric cars catching fire/exploding comes up - not because it isn't possible, but because the car in your driveway *right now* has lots of explosive material in it (gasoline for starters). Ford has issued a number of recalls (on the Fusion, Escape, and before that on the Expedition) for cars spontaneously catching fire. This is a problem faced by all manufacturers, so it isn't surprising it would be faced when dealing with new technology like the Volt, or Fisker Karma. It is a question of relative risk, and I don't think we have enough data (and it is likely that these technologies will improve over time).

Voldenuit wrote:Wow, so the FAA has approved the certification plan for the battery fix. To be clear, this just means they're approving Boeing to move on the the next stage of testing on the redesigned battery containment and isolation system, not necessarily approving the fix itself. If and when it is proved safe, then the changes would be approved and the plane recertified to fly.

Although I went on record as saying that this fix would be the quickest and most expedient way for Boeing to get the planes back in the air, I must admit that I am a bit disappointed in the FAA here. I was honestly expecting them to kick the idea back to the curb. The problem is that I frankly think this is a stopgap solution (as I said earlier), but that the management at Boeing doesn't seem to realise this. Once this is approved, they are likely to stop working on a more permanent solution until the next disaster happens.

Blegh.

If planes aren't flying/aren't rolling off an assembly line, Boeing isn't making any money. Fixes on complicated vehicles like these typically come in two phases: containment and resolution. If they contain it, they can get back to making money, but that doesn't mean they'll stop working on more permanent fixes. Engineers are going to tell them when a solution contains the problem without really fixing it.

And for reference, I work in the heavy truck industry. I've handled these kind of issues.

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FireGryphon wrote:Maybe this needs to be split off into another thread, but what is the benefit of having electric power over hydraulic design for control surfaces? It seems that in the event of Things Going Horribly Wrong, you'd want the plane to rely on as little electronics as possible.

Hydraulic plumbing, accumulators, pumps etc weigh more that electric wires. There's also the problem of ensuring everything is sealed and running at the right pressures in hydraulics. The engines have to generate electricity anyway so it's not too hard to rip out the hydraulic pumps and upsize the generators in the design phase. Less weight in the plane bits means you can carry more weight of passengers or fuel.

As for when things go wrong, there were the same arguments when they went from cable controls to hydraulic - you can always come up with a scenario where one will work and the other will not but it is a question of probabilities of occurrence. The Boeing 737 rudder reversal issue was with hydraulic controls.

FireGryphon wrote:Maybe this needs to be split off into another thread, but what is the benefit of having electric power over hydraulic design for control surfaces? It seems that in the event of Things Going Horribly Wrong, you'd want the plane to rely on as little electronics as possible.

Hydraulic plumbing, accumulators, pumps etc weigh more that electric wires. There's also the problem of ensuring everything is sealed and running at the right pressures in hydraulics. The engines have to generate electricity anyway so it's not too hard to rip out the hydraulic pumps and upsize the generators in the design phase. Less weight in the plane bits means you can carry more weight of passengers or fuel.

As for when things go wrong, there were the same arguments when they went from cable controls to hydraulic - you can always come up with a scenario where one will work and the other will not but it is a question of probabilities of occurrence. The Boeing 737 rudder reversal issue was with hydraulic controls.

Actually, with electronics you could go the path of triple redundancy, too. I have no idea if they actually do this, but if you put three copies of an electronic control system on a plane, you can have up to two of them fail and still fly safely, all without adding too much to the weight of the plane.

"A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP"

superjawes wrote:Actually, with electronics you could go the path of triple redundancy, too. I have no idea if they actually do this, but if you put three copies of an electronic control system on a plane, you can have up to two of them fail and still fly safely, all without adding too much to the weight of the plane.

They already do that with hydraulics, works well until you have a turbine disk burst and sever all 3 systems like in the Sioux City DC-10 crash.